Wet electrostatic precipitators have been used for many years to remove dust, acid mist and other particulates from water-saturated air and other gases by electrostatic means. In a WESP, particulates and/or mist laden water-saturated air flows in a region of the precipitator between discharge and collecting electrodes, where the particulates and/or mist are electrically charged by corona emitted from high voltage discharge electrodes. As the water-saturated gas flows further within the WESP, the charged particulate matter and/or mist is electrostatically attracted to grounded collecting plates or electrodes where it is collected. The accumulated materials are continuously washed off by both an irrigating film of water and periodic flushing.
WESPs are used to remove pollutants from gas streams exhausting from various industrial sources, such as incinerators, wood products manufacturing, coke ovens, glass furnaces, non-ferrous metallurgical plants, coal-fired electricity generation plants, forest product facilities, food drying plants and petrochemical plants.
Traditionally, the collecting surfaces and other parts of electrostatic precipitators exposed to the process gas stream have been fabricated from carbon steel, stainless steel, corrosion and temperature resistant alloys and lead. However, such materials tend to corrode and/or degrade over time especially when the precipitators are used in severe environments. Carbon and stainless steel tend to corrode or erode under severe acid conditions. Reinforced thermoplastics tend to erode and/or delaminate due to severe corrosive conditions and localized high temperature in regions of sparking.
Other methods have been used to fabricate collecting surfaces involving the use of plastic materials; however, these materials rely on a continuous water film to ensure electrical grounding of the equipment, which has proved to be a problem. PVC, polypropylene and other similar materials have been used but have suffered from holes and flashover-induced fires and, therefore, are not widely used.
In PCT publications Nos. WO2008/154,735 and WO2010/108,256, assigned to the assignee hereof and incorporated herein by reference, there is described electrically-conductive, corrosion resistant and temperature and spark resistant composite material with good heat dissipation for use in the fabricating components used in WESPs. Such materials generally comprise carbon fiber with a thermosetting resin in a cross-linked structure.
As described therein, the electrically conductive composite material utilized herein is a conductive composite material designed for highly corrosive operating conditions including dry and saturated mist environments with elevated temperatures. The composite material is a blend of carbon fibers and thermosetting resins developed for wet electrostatic precipitation, where such materials are subjected to corona voltage flash over, spark, erosion, corrosion and power arc.
In particular, the composite material comprises carbon fiber within a thermosetting resin where extremely strong molecular building blocks form totally cross-linked structures bonded to each other and at interconnects. The resultant network has proven to withstand high voltage current after the onset of corona in the tubes of the electrostatic precipitator, obtaining voltage flash over without pitting the conductive hybrid composite material. Such spark resistance and arc-over may be generated at a voltage of approximately 60 to 95 KV at up to 500 to 1000 milliamps for a duration of approximately 1 millisecond. The composite material is also resistant to sustained arcing with a duration of up to 4 to 5 seconds. These properties are highly desirable to minimize corrosion and restrict high intensity heat generation and to prevent structural, mechanical or chemical changes to the conductive hybrid composite material.
The carbon fibers woven into a seamless biaxial material sleeve creates a dense network imparting electrical conductivity and thermal dispersion within thermosetting resins.
Strong molecular building blocks form totally cross-linked structures bonded to each other and as interconnects, producing a three-dimensional network, stitched through the thickness of the laminate. The carbon fibers are woven into seamless biaxial and triaxial material. This arrangement imparts excellent electrical conductivity and superior thermal dispersion through the laminate.
In addition to the electro-conductive characteristics and excellent corrosion resistant properties, the conductive hybrid composite material also provides further advantages as a material of construction, reducing the dead load weight by one half or more, due to the lightweight and high strength qualities of carbon fiber which results in economic benefits before installation especially beneficial for tube bundles made from stainless steel and even higher grades of titanium.
The composite may be prepared by weaving, stitching, alignment through vibration using frequency while the material may be formed into shapes that are tubes and sheets by prior art processes known as vacuum infusion, pultrusion, filament winding and autoclaving.
The conductive composite material overcomes the problems of corrosion affecting stainless steel, alloys and titanium within a highly corrosive environment, saturated mists and elevated temperatures, by improving on prior art thermosetting resins and carbon fiberglass compositions that cannot withstand the corona voltage flash over and power arcs at up to 100,000 Volts.